Computer based system. Need advice on DAC.

Get a dac with a volume control. It will allow you to get rid of that old preamp. Removing the preamp will probably make a bigger difference than the dac itself.

I would agree with Zd. However it may be more expensive to buy a DAC with a good volume control which is analog. Another idea is to use a simple device from shiit audio that is simply a passive volume control. That would give you the option of a second source such as a CD player or turntable and you could buy the DAC of your choice.

I recently bought a Teac UD-301. I couldn't be more happy. Reasonable priced. Works with my MacBook Pro and Raspberry Pi. Has balanced outs, which I connected to my Jolida 502CRC. And it is on a $100 rebate until the end of the month. Check it out. http://audio.teac.com/product/ud-301/

I use a Sonore exD, which I really enjoy. 1300 MSRP; got mine much cheaper used. Sonically comparable to the PSA Perfect Wave Mk 2 it replaced.

In generally, I now lean away from spending a lot on a DAC. Differences in upgrades are often quite incremental, and technology is changing daily -- meaning you'll likely want to try new things, and there a good bit of high quality "yesterday's gear" on the used market.

My experience useing the PSA as a preamp was very underwhelming (although the PSA implementation is digital, and the subject of criticism). I think you'll here plenty on both sides of this question.

In your position, I'd get the best DAC I could afford, and plan, as you are, on upgrading amplification later.

If the DAC you select has a volume control and you enjoy that set up, call it a bonus.

John